1. Field of the Invention
The present invention relates to an output regulation circuit and more specifically relates to an output regulation circuit of a power converter without current sensing loss.
2. Description of Related Art
Resistor-based current sensing is simple, easy to use, low-cost, extremely linear, and requires no calibration. Ohm's Law states that voltage across a resistor is directly proportional to the current through it: V=IR. As a caveat, however, note that all resistors dissipate power when current passes though them. Because the dissipation produces heat that, in turn, affects the resistance, power dissipation in a sensing resistor must be carefully assessed.
FIG. 1 shows a conventional current sensing circuit of the power converter. A sensing resistor 12 is coupled to the power switch 11 of the power converter 10. In continuous conduction mode operation, when the power switch 11 enables, the input voltage excites the transformer 13. Hence, the input current Ip is increased, and transforms to a voltage signal Vref by the sensing resistor 12. The comparator 141 of the control IC 14 receives the voltage signal Vref to compare with a feedback signal Vfeb. When the current reaches the predetermined value, the power switch 11 disables. Until the next period, the power switch 11 will enable to output energy steady.
Due to the sensing resistor 12 exists in the main power loop, the power dissipation in the sensing resistor 12 is depends on the current. The current is greater, and the loss will increase. Therefore, a need exists for a lossless method to sense current.